1. Field of the Invention
The present invention relates generally to a metal material for plastic processing and to a processing method for forming a bent and deformed portion in the same.
2. Related Background Art
In forming, for example, an angle-shaped bent and deformed portion in a metal material such as a strip-like material, a flat plate material, or the like, generally used methods include roll forming, push and bend forming, thrust bend forming, press-forming, or the like.
In addition, in the case of forming a special article such as a transverse frame for supporting a color selection electrode (a shadow mask) inside a cathode-ray tube, for instance, a round steel stick is subjected to hot rolling to have a predetermined angle shape and the shape is adjusted by drawing. Annealing then is performed, thus obtaining a product.
In a conventional processing method, however, only products with bent and deformed portions whose thickness is uniform throughout can be formed. Therefore, when such a product is to be applied to a member required to have a strength to a certain degree such as the above-mentioned frame for supporting the color selection electrode, the member becomes heavy inevitably.
When employing the above-mentioned rolling and drawing, high pressure and a great amount of heat are required in rolling, and an annealing step also is required. Consequently, not only the size of equipment as a whole and the production cost increase, but also a longer time is required for the processing and cracks may occur in the case of improper annealing.
It is an object of the present invention to provide a metal material for plastic processing, which can contribute to the reduction in weight of a product while maintaining substantially the same strength as that of a conventional product, can be processed economically with relatively simple steps, and provides an excellent final product, and to provide a processing method for forming a bent and deformed portion in the metal material.
In order to achieve the aforementioned objects, the present invention employs the following configurations.
In the method of the present invention, first, a metal material is rolled to form a strip plate material having a middle part and thinner thickness-deviation portions on both sides of the middle part. After that, this strip plate material is bent and deformed in its width direction by roll forming, thus forming a bent and deformed portion in the middle part.
According to the above-mentioned processing method, the bent and deformed portion formed by the roll forming has at least the same thickness as an original thickness of the metal material, and the thickness-deviation portions positioned on both sides of the bent and deformed portion are formed to be thinner in a rolling step prior to the roll forming. Therefore, while maintaining substantially the same strength as that of a conventional product, a plastically formed article with the bent and deformed portion can have a reduced weight.
Since the method of the present invention includes the rolling step and the roll forming step, the metal material can be processed economically using relatively simple steps. Moreover, no annealing step is included, and therefore an excellent final product can be obtained.
The quality and shape of the metal material are not particularly limited as long as the metal material is a steel material or another metal material suitable for plastic processing.
In the rolling step for forming the strip plate material from the metal material, thickness-deviation portions are formed to be reduced in thickness gradually from the middle part toward the ends of side portions positioned on both sides of the middle part. Furthermore, at a predetermined position in the middle part corresponding to an outer corner of a bent and deformed portion to be formed, a thick stripe portion is formed suitably. The thick stripe portion may be formed of one stripe, but also may be formed of two adjacent protruding stripes extending continuously along the length direction in the middle part of the strip plate material with the portion between the two protruding stripes being recessed in an arc shape. In the strip plate material with the middle part formed to be thicker than the thickness-deviation portions, the middle part is bent and deformed in its width direction by the roll forming and thus the bent and deformed portion is formed. In the rolling or the roll forming, a tapered face or a thick protruding portion may be formed at one or both of the ends of the thickness-deviation portions as required. According to the method of the present invention, the tapered face or the protruding portion, which has been provided in an independent step conventionally, also can be formed in the rolling step or the roll forming step, thus simplifying the steps.
For the rolling, warm rolling can be employed. However, it is preferable that rolling under ordinary temperature (cold rolling) is employed and the next step of roll forming is carried out while processing heat generated during the cold rolling still remains in the strip plate material. In other words, the rolling step and the roll forming step are carried out successively and therefore the roll forming can be carried out with high efficiency using the processing heat generated during the rolling.
It also is possible that the above-mentioned rolling step and roll forming step are not carried out as two separate steps but concurrently at substantially the same time.
In other words, while thinner thickness-deviation portions are formed on both sides of a middle part of a metal material by rolling of the metal material, the metal material may be bent and deformed in its width direction by roll forming to form a bent and deformed portion in the middle part. Furthermore, in forming the thickness-deviation portions, a thick stripe portion also may be formed at a predetermined position in the middle part corresponding to an outer corner of a bent and deformed portion to be formed, thus bending and deforming the metal material at a position of the thick stripe portion.
Even when the metal material is bent and deformed by roll forming while the thickness-deviation portions (and further the thick stripe portion as required) are formed by rolling as described above, the same effects as in the above can be obtained. Moreover, when the both steps are carried out concurrently, the forming steps can be simplified and the processing heat generated during the rolling can be used for the roll forming effectively, thus improving formation efficiency.
A metal material for plastic processing of the present invention is a material obtained after the completion of the above-mentioned rolling step. The metal material is formed of a metal plate having a middle part in its width direction and thinner thickness-deviation portions on both sides of the middle part, and the middle part is formed to be a bent and deformed portion.
Another metal material for plastic processing of the present invention is formed of a metal plate having a middle part in its width direction and thinner thickness-deviation portions on both sides of the middle part and also having a thick stripe portion at a predetermined position in the middle part corresponding to an outer corner of a bent and deformed portion to be formed, and the middle part is formed to be the bent and deformed portion.
When a bent and deformed portion is formed by roll forming or the like using such a metal material, an angle member with a reduced weight can be obtained while having the same strength as that of a conventional one.
The angle member thus obtained can be used as a supporting frame for a color selection electrode in a cathode-ray tube or a frame for reinforcement in an automobile.